Rust busting! Heating system water quality

3 Stage micron filter

Practical Guide to Managing Corrosion and Water Quality in Heating Systems

This post is a bit of a work in progress. Having invested heavily in heating system water quality equipment, had a great chat with Ricky at thoroughflush uk and studied the heat geek article I felt it was time to get really clear on our best practice for managing this issue. Here goes..!

Corrosion and poor water quality are among the biggest challenges in maintaining efficient and long-lasting heating systems. Whether you're a heating engineer or a homeowner, knowing how to manage these issues can save you time, energy, and money in the long run.

In this guide, we’ll break down the practical steps you can take to reduce corrosion, improve heating system performance, and ensure compliance with best practices like VDI 2035 all without overcomplicating things or getting too theoretical.

Why Does Heating System Water Matter?

Heating systems rely on clean, balanced water to transfer heat efficiently. However, over time, corrosion and scaling can lead to problems like:

• Reduced efficiency (e.g., less heat at radiators or higher energy bills).

• System failures due to damaged components like boilers, heat exchangers, diverter valves or radiators.

• Increased maintenance costs from clogged pipes, sludge, or leaks.

By managing water quality and corrosion effectively, you can extend the life of your system and ensure it performs at its best.

Photo of 3 month old ESBE diverter valve that seized due to poor water quality.

The Alpine Heating Standard Process for Water Quality Management

Our take on all the guidance resulting in our process for managing heating system water quality involves the following steps:

1. Build and Fill: Assemble the system and fill it with water, using either tap water or pre-treated water depending on local water quality. Install and open automatic air vents to remove trapped air during filling.

2. Initial Corrosion Period: Allow the system to operate for a few days. During this time, the initial corrosion will occur, and oxygen will react with metals to create a passive layer. This thin layer of corrosion protects deeper layers of metal from further damage.

3. Flush or Filter: After (or during in the case of filtering) the initial corrosion period, either:

- Perform a full flush to remove debris, loose rust particles, and contaminants.

- OR install a fine particle filter (e.g., 25/10/5 micron) to capture rust and debris without wasting water. Filtering is particularly useful for conserving water or when frequent draining is impractical.

4. Demineralise: If the water quality is poor (e.g., high hardness or conductivity), use the demineralisation unit to reduce dissolved salts and minerals, ensuring the system water is clean and compliant with standards (ie VDI 2035).

5. Close or Isolate Auto Air Vents: Once the system has been filled, flushed, or filtered and commissioned, close or isolate the automatic air vents to prevent oxygen ingress. Leaving vents open is a common source of ongoing corrosion.

6. Verify: Ensure it is properly sealed, and record the conductivity and pH levels.

This method ensures that the system starts clean, operates efficiently, and minimizes scaling and corrosion risks.

How Auto Air Vents Can Cause Problems

While automatic air vents are useful during the initial filling and commissioning phase, they can also act as a source of oxygen ingress if left open or malfunctioning:

• Oxygen Ingress Risk: If the vent doesn’t close properly, air can enter the system, bringing fresh oxygen that accelerates corrosion.

• Pressure Changes: During pressure drops (e.g., cooling cycles or leaks), oxygen can be drawn into the system through the vent.

• Compounding Corrosion: Oxygen increases water conductivity, disrupts the protective passive layer on metals, and creates a vicious cycle of corrosion.

Why Measuring Oxygen Content Is Impractical

Testing the oxygen content in heating systems is technically possible but highly impractical for several reasons:

1. Exposure to Air: The moment you remove water from the system to test it, it comes into contact with atmospheric air, which skews the results by adding oxygen.

2. Specialised Equipment: Measuring dissolved oxygen requires expensive equipment that isn’t cost-effective for most domestic or small commercial systems.

3. Better Indicators: Instead of directly testing oxygen, you can monitor the system indirectly by:

- Checking conductivity: Rising conductivity may indicate oxygen-driven corrosion.

- Observing debris: Increased rust or sludge in filters suggests ongoing oxygen ingress.

By focusing on controlling oxygen ingress (e.g., closing vents, using oxygen-tight materials), you can minimize its impact without needing to measure it directly.

Best Practices for Managing Auto Air Vents

To prevent oxygen ingress from auto air vents:

1. Close or Isolate After Commissioning: Once the system is operational and the initial air has been purged, ensure all automatic air vents are capped or sealed.

2. Inspect Regularly: Check vents for signs of wear or malfunction and replace any that fail to close properly.

3. Use Manual Air Vents When Possible: In sealed systems, manual vents can eliminate the risk of ongoing oxygen ingress while still allowing trapped air to be released during maintenance.

Should You Demineralise Before Turning on a Heat Pump?

If you’re installing a heat pump, it’s better to demineralise the water before turning it on. Here’s why:

• Heat pumps typically operate at lower flow temperatures, but the surfaces of their heat exchangers can still reach high enough temperatures to bake scale onto the surface. This happens particularly in hard water areas.

• Once scale is baked onto a heat exchanger, it forms an insulative layer that reduces heat transfer efficiency, leading to higher energy bills and potential system damage.

By demineralising the water before commissioning the heat pump, you prevent scale formation from the start, ensuring the system runs as efficiently as possible.

Key Takeaways

1. Follow the Standard Process: Build, fill, let the system settle, flush or filter, demineralise, close auto air vents, and then commission.

2. Test the Water: Measure conductivity and pH; skip direct oxygen testing as it’s impractical. Use conductivity and rust/debris as proxies for oxygen ingress.

3. Demineralise When Needed: Prevent scaling by using demineralised water, especially for heat pumps or in hard water areas.

4. Reduce Oxygen Ingress: Use oxygen-tight pipes, seal the system properly, and close or cap auto air vents after commissioning.

5. Flush or Filter Debris: Remove sludge and debris to maintain system performance.

By following these steps and managing auto air vents carefully, you can ensure your heating system operates efficiently, lasts longer, and requires less maintenance—all while avoiding unnecessary intervention costs or complications.